Method of producing all skin rayon



United States Patent 3,049,398 METHOD OF PRODUCING ALL SKIN RAYON Byron A. Thumm, Delaware County, Pa., assignor to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Original application Dec. 5, 1955, Ser. No. 550,826, now Patent No. 2,932,578, dated Apr. 12, 1960. Divided and this application Sept. 23, 1959, Ser.

11 Claims. (Cl. 18-54) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthate is subsequently dis solved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filamen-t may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods consist of a skin or outer shell portion and a core portion with a sharp line of demarkation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent differences in structure and these different portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subject to fibrillation and is relatively stiff.

It has now been discovered that the presence of small amounts of alkali-soluble alkylene oxide adducts of 2- aminopyridine in the viscose results in the production of shaped bodies of regenerated cellulose such as filaments, films, sheets and the like composed of all skin and having improved properties and characteristics providing that the amount of the adduct is maintained within certain limits and the composition of the spinning bath is maintained within certain composition limits which will be defined herein-after. The most readily distinguishable characteristic as compared to conventional filaments includes a smooth, non-crenulated surface and the filaments consist entirely of skin.

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The alkylene oxide adducts may be prepared by reactmg Z-aminopyridine with an alkylene oxide such as ethylene oxide or propylene oxide, the amino hydrogen atoms being replaced by a polyoxyethylene glycol radical. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water and alkali solutions such as a 6% caustic solution, the ethylene oxide adducts are preferred. Accordingly, the invention will be illustrated by reference to the ethylene oxide adducts.

The alkylene oxide content of the adducts may vary from an average. of about 4 to 100 or more alkylene oxide units per molecule of Z-aminopyridine, the preferred materials containing from about 5 to about 40 alkylene oxide units. It is not essential that each of the polyoxyalkylene radicals or groups be of the same length.

The amount of the alkylene oxide adduct of 2-aminopyridine which is incorporated in viscose must be at least about 0.3% by weight of the cellulose in the viscose and may vary up to about 4%, preferably, the amount varies from about 0.5% to 2%. Lesser amounts do not result in the production of products consisting entirely of skin and greater amounts affect adversely the physical properties of the products. Amounts vw'thin the preferred range are most effective in enhancing the characteristics and properties of the products. The adduct or modifier may be added at any desired stage in the production of the viscose such as in the preparation of the refined wood pulp for the manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The adduct or modifier is preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose may contain from about 4% to about 10% cellulose, the particular source of the cellulose being selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight of the cellulose. The modified viscose, that is, a viscose containing the small amount of an alkylene oxide adduct cf Z-aminopyridine, may have a salt test above about 8 and preferably above about 9 at the time of spinning or extrusion.

In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinning bath be maintained within a well defined range. The presence of the alkylene oxide adduct of Z-aminopyridine in the viscose combined with these limited spinning baths results in the production of yarns of improved properties such as high tenacity, high abrasion resistance, high fatigue resistance and consisting of filaments composed entirely of skin.

Generically, and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath. The bath should contain from about 10% to about 25 sodium sulfate and from about 3% to about 15% zinc sulfate, preferably from 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about C., preferably between about 45% C. and about 70 C. In the production of the all skin type filaments, the temperature of the spinning bath is not critical, however, as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about 55 C. and 65 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. For commercial operations, the acid concentration of the spinning bath is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the point at which the neutralization of the caustic of the viscose is sufficiently rapid to form a filament having a skin and core.

There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is sufliciently rapid to produce filaments having a skin and core. For example, in general, the acid concentration of the spinning baths which are satisfactory for the production of the all skin products from a 7% cellulose, 6% caustic-viscose and containing ethylene oxide adducts of Z-aminopyridine in the small amounts stated lies between about 6% and about 7.5%. The acid concentration may be increased as the amount of adduct is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of adduct and the concentration of caustic in the viscose. Ail skin products cannot be obtained if the acid concentration is increased above the maximum value although the amount of aminopyridine is increased beyond about 4% while other conditions are maintained constant. Increasing the caustic soda content of the viscose beyond about 8% is uneconomical for commercial production methods. For example, a viscose containing about 7% cellulose, about 6.5% caustic soda, about 36% (based on the weight of cellulose) carbon disulfide, and 1% (based on the weight of cellulose) of an ethylene oxide adduct of 2-aminopyridine and containing about 20 ethylene oxide units and having a salt test of about 9 when extruded into spinning baths containing 16 to 20% sodium sulfate, 4 to 8% zinc sulfate and sulfuric acid not more than about 7.8%, results in the production of all skin filaments. Lesser amounts of sulfuric acid may be employed. Greater amounts of sulfuric acid result in the production of products having skin and core. A lowering of the amount of the adduct or modifier, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of all skin filaments. It has been determined that the maximum concentration of acid which is permissible for the production of all skin products is about 8%.

The presence of the adduct in the viscose retards the coagulation and, therefore, the amount of adduct employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and at a spinning speed of about 50 meters per minute, the adduct is employed in amounts within the lower portion of the range, for example, about 0.5%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period sufiicient to effect relatively complete coagulation of the viscose, that is, the coagulation must be sufficient so that the filaments will not adhere to each other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about 70% to 120%, preferably between 75% and Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of alkylene oxide adducts of Z-aminopyridine and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the cross-section of the filament. Filaments produced pursuant to this invention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments prepared from viscose containing the adducts have superior abrasion and fatigue resistance characteristics and have a high flex-life as compared to normal regenerated cellulose filaments. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic tire casings, but the filaments are not restricted to such uses and may be used for other textile applications.

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a viscose containing about 7.4% cellulose, about 6.6% caustic soda, and having a total carbon disulfide content of about 36% based on the weight of the cellulose. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 36% carbon disulfide based on the weight of the cellulose and churning for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. The desired amount of the ethylene oxide adduct of 2-aminopyridine was added to the solution and mixed for about ,6 hour. The viscose was then allowed to ripen for about 28 hours at 18 C.

Example 1 Approximately 0.5% of an ethylene oxide adduct of 2-aminopyridine containing 20 ethylene oxide units per molecule (based on the weight of the cellulose) was added to and incorporated in the viscose as described above. The viscose employed in the spinning of filaments had a salt test of 9.2. The viscose was extruded through a spinneret to form a 200 denier, 100 filament yarn at a rate of about 22 meters per minute. The coagulating and regenerating bath was maintained at a temperature of about 60 C. and contained 7.6% sulfuric acid, 5% zinc sulfate and 17% sodium sulfate. The yarn was stretched about 82% while passing through a hot water bath maintained at 95 C. The yarn was collected in a spinning box, washed free of acids and salts and dried.

The individual filaments have a smooth, non-crenulated exterior surface and consist entirely of skin, no core being detectable at high magnification (e.g. l500 The filaments of a control yarn (Example 3) spun with the same viscose but without the addition of the modified agent and spun under the same conditions, exhibit a very irregular and serrated surface and are composed of about 60% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 2 To a viscose as described above, there was added 1% of the adduct described in Example 1. The viscose had a salt test of 9.4 and was spun into a 200 denier, 100 filament yarn by extrusion into a spinning bath containing 7.6% sulfuric acid, 5% zinc sulfate and 17% sodium sulfate. The bath was maintained at 60 C. and the extrusion rate was about 22 meters per minute. The filaments were subsequently passed through a hot water bath at 95 C. and stretched about 82%. The yarn was collected in a spinning box, washed free of acids and salts and dried.

The individual filaments were readily distinguishable from control filaments (Example 3) in that they have a smooth, non-crenulated surface and consist entirely of skin while the control filaments have a very irregular and serrated surface and consist of about 60% skin and the balance core with a sharp line of demarkation between the skin and the core. Other physical properties are set forth in the table which follows the examples.

Example 3 A viscose solution as described above (no modifier added) having a salt test of 9.5 was spun into a 200 denier, 100 filament yarn by extrusion into a spinning bath containing 7.6% sulfuric acid, 5% zinc sulfate and 17% sodium sulfate. The bath was maintained at 60 C. and the extrusion rate was about 22 meters per minute. The filaments were passed through a hot water bath maintained at about 95 C. and stretched about 82%. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The filaments have a smooth, non-crenulated surface and consist entirely of skin while control filaments have a very irregular and serrated surface and consist of about 60% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical characteristics are set forth in the table which follows:

Tenacity, Elongation, Gramsper denier percent Skin,

percent Wet Dry Wet Dry Example 1 2. 2 3. l 25 20 100 Example 2 2. 3 3. l 25. 18 100 Example 3 (Control) 1. 9 2. 8 22 18 60 sess improved abrasion resistance, flex-life and other properties as disclosed hereinbefore. If desired, small amounts of the adducts may be added to the spinning bath. Since the adducts are water-soluble, some of the ether will be leached from the filaments or other shaped body and will be present in the bath.

One of the properties of viscose rayon which has lim ited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65% to about for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

The alkylene oxide adducts of Z-aminopyridine may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The adducts may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportions of the adduct at the time of spinning.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for l to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

In the foregoing disclosure, the modifier has been termed an alkylene oxide adduct of 2-aminopyridine. More technically, the compounds may be termed di- (omega-hydroxy polyoxyalkylene)alpha-pyridyl amines and correspond to the formula where n is 2 or 3, x and y are whole numbers and the sum of x and y varies from 4 to or more, preferably from about 5 to about 40. It is possible that these adducts or compounds have hydroxy polyoxyalkylene chains of different lengths and that the alkylene oxide units are not in all cases equally distributed on the amino nitrogen. The average alkylene oxide content may be expressed as the number of alkylene oxide units per molecule of alpha pyridyl amine.

This application is a division of my copending application Serial No. 550,826, filed December 5, 1955, entitled Method of Production All Skin Rayon, now Patent No. 2,932,578, dated April 12, 1960.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the step which comprises extruding viscose containing a small amount, based on the weight of the cellulose in the viscose, of a modifying agent into an aqueous spinning bath containing from about 10% to about 25% sodium sulfate, from about 3% to about 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but being below the concen-' tration at which neutralization of the caustic soda of the viscose is sufficiently rapid so as to produce shaped bodies consisting of skin and core, the modifying agent being a di(omega-hydroxy polyoxyalkylene)alpha-pyridyl amine wherein the alkylene oxide is selected from the group consisting of ethylene oxide and propylene oxide and the amine contains from about 4 to 100 alkylene oxide units, said small amount of the modifying agent being a quantity sufiicient to impart a smooth, non-crenulated surface and a substantially all skin structure to products formed by spinning the viscose at a sodium chloride salt test of at least 9 into an aqueous bath containing from 15 to 22% sodium sulfate, from 4% to 9% zinc sulfate and sulfuric acid in an amount not exceeding 8%, but the quantity being insufficient to adversely affect the physical properties of such products.

2. The step in the method as defined in claim 1 wherein the alkylene oxide in the modifying agent is ethylene oxide.

3. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the step which comprises extruding viscose containing from about 0.3% to about 4%, based on the weight of the cellulose in the viscose, of a modifying agent into an aqueous spinning bath containing from about 10% to about 25 sodium sulfate, from about 3% to about 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 8%, the modifying agent being a di(omega-hydroxy polyoxyalkylene)alpha-pyridyl amine wherein the alkylene oxide is selected from the group consisting of ethylene oxide and propylene oxide and the amine contains from about 4 to 100 alkylene oxide units.

4. 'I:he step in the method as defined in claim 3 wherein the alkylene oxide in the modifying agent is ethylene oxide.

5. The step in the method as defined in claim 3 wherein the alkylene oxide in the modifying agent is ethylene oxide and the modifying agent contains from about 5 to about 40 ethylene oxide units per molecule of the amine.

6. In a method of producing shaped bodies of regenerated celluloseconsisting substantially entirely of skin, the steps which comprise adding to and incorporating in viscose a small amount, based upon the weight of the cellulose in the viscose; of a modifying agent and extruding the viscose into an aqueous spinning bath containing from about to about 25% sodium sulfate, from about 3% to about zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but being below the concentration at which neutralization of the caustic soda of the viscose is sufficiently rapid so as to produce shaped bodies consisting of skin and core, the modifying agent being a di(omega-hydroxy polyoxyalkylene) alpha-pyridyl amine wherein the alkylene oxide is selected from the group" consisting of ethylene oxide and propylene oxide. and the amine contains from about 4 to 100 alkylene oxide units, said small amount of the modifying agent being a quantity suflicient to impart a smooth, non-crenulated surface and a substantially all 8 skin structure to products formed by spinning the viscose at a sodium chloride salt test of at least 9 into an aqueous bath containing from 15% to 22% sodium sulfate, from 4% to 9% zinc sulfate and sulfuric acid in an amount not exceeding 8%, but the quantity being insufiicient to adversely affect the physical properties of such products.

7. The steps in the method as defined in claim 6 wherein the alkylene oxide in the modifying agent is ethylene oxide and the modifying agent contains from about 5 to about 40 ethylene oxide units per molecule of the amine.

8. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the steps which comprise adding to and incorporating in viscose from about 0.3 to about 4%, based on the weight of the cellulose in the viscose, of a modifying agent and extruding the viscose into an aqueous spinning bath containing from about 10% to about 25% sodium sulfate, from about 3% to about 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 8%, the modifying agent being a di(omega-hydroxy polyoxyalkylene)alpha-pyridyl amine wherein the alkylene oxide is selected from the group consisting of ethylene oxide and propylene oxide and the amine contains from about 4 to alkylene oxide units.

9. The method as defined in claim 8 wherein the alkylene oxide in the modifying agent is ethylene oxide and the'modifying agent contains from about 5 to about 40 ethylene oxide units per molecule of the amine.

10. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in a viscose from about 0.3% to about 4%, based upon the weight of the cellulose in the viscose, of a modifying agent, ripening the viscose to a salt point of not less than 8 and extruding the viscose into an aqueous spinning bath containing from about 16% to about 20% sodium sulfate, from about 4% to about 9% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but being below the concentration at which neutralization of the caustic soda of the viscose is sufficiently rapid so as to produce shaped bodies consisting of skin and core, the modifying agent being a di(omega-hydroxy polyoxyalkylene)alpha-pyridyl amine wherein the alkylene oxide is selected from the group consisting of ethylene oxide and propylene oxide and the amine contains from about 4 to 100 alkylene oxide units.

11. The method as defined in claim 10 wherein the alkylene oxide in the modifying agent is ethylene oxide and the modifying agent contains from about 5 to about 40 ethylene oxide units per molecule of amine.

References Cited in the file of this patent UNITED STATES PATENTS 2,593,466 MacLaurin Apr. 22, 1952 2,648,611 Richter Aug. 11, 1953 2,705,184 Drisch Mar. 29, 1955 2,732,279 Tachikawa Jan. 24, 1956 2,810,658 Pontius Oct. 22, 1957 2,840,448 Thumm ..L'.. June 24, 1958 2,853,360 Thumm Sept. 23, 1958 2,906,634 Sisson Sept. 29, 1959 

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE CONSISITING SUBSTANTIALLY ENTIRELY OF SKIN, THE STEP WHICH COMPRISES EXTRUDING VISCOSE CONTAINING A SMALL AMOUNT, BASED ON THE WEIGHT OF THE CELLULOSE IN THE VISCOSE, OF A MODIFYING AGENT INTO AN AQUEOUS SPINNING BATH CONTAINING FROM ABOUT 10% TO ABOUT 25% SODIUM SULFATE, FROM ABOUT 3% TO ABOUT 15% ZINC SULFATE AND SULFURIC ACID, THE SULFURIC ACID CONTENT OF THE SPINNING BATH EXCEEDING THE SLUBBING POINT BUT BEING BELOW THE CONCENTRATION AT WHICH NEUTRALIZATION OF THE CAUSTIC SODA OF THE VISCOSE IS SUFFICIENTLY RAPID SO AS TO PRODUCE SHAPED BODIES CONSISTING OF SKIN AND CORE, THE MODIFYING AGENT BEING A DI(OMEGA-HYDROXY POLYOXYLALKYLENE)ALPHA-PYRIDYL AMINE WHEREIN THE ALKYLENE OXIDE IS SELECTED FROM THE GROUP CONSISTING OF ETHYLENE OXIDE AND PROPYLENE OXIDE AND THE AMINE CONTAINS FROM ABOUT 4 TO 100 ALKYLENE OXIDE UNITS, SAID SMALL AMOUNT OF THE MODIFYING AGENT BEING A QUANTITY SUFFICIENT TO IMPART A SMOOTH, NON-CRENULATED SURFACE AND A SUBSTANTIALLY ALL SKIN STRUCTURE TO PRODUCTS FORMED BY SPINNING THE VISCOSE AT A SODIUM CHLORIDE SALT TEST OF AT LEAST 9 INTO AN AQUEOUS BATH CONTAINING FROM 15% TO 22% SODIUM SULFATE, FROM 4% TO 9% ZINC SULFATE AND SULFURIC ACID IN AN AMOUNT NOT EXCEEDING 8%, BUT THE QUANTITY BEING INSUFFICIENT TO ADVERSELY AFFECT THE PHYSICAL PROPERTIES OF SUCH PRODUCTS. 